1. Field of the Invention
A heat producing pack utilizing an outer bag and a removable inner bag which contains a chemical composition to produce an exothermic reaction when moistened.
2. Description of the Prior Art
It has long been known that the combination of certain chemical elements produces an exothermic reaction. Many such combinations include ferrous materials such as iron filings and other chemicals which release heat when they are combined with an aqueous solution. Such chemical compositions are frequently utilized in combination with a bag-like container to form a heating pack which can be selectively activated by adding water to the chemical composition and deactivated by allowing the chemical composition to dry.
Presently available chemical-composition heating packs are frequently limited in their usefulness either by the limited amount of heat per unit weight which the chemical composition yields when reacting with water, by the useful life of the chemical composition, or by the structure of the bag which contains the chemical composition. In particular, when a ferrous material is utilized as part of the chemical composition, the overall weight of the heating pack is increased significantly. In the past, the limitations on efficiency of the oxidizing mixture utilized with the ferrous material have required a relatively large amount of the ferrous material and thus the weight of the heating pack has frequently been a limiting factor in the design of such devices. Because of the limitations in the efficiency of the oxidizing mixture, the heat output of the heating pack frequently could be increased only by significantly increasing the amount of ferrous material which is utilized. In addition to adding weight to the heating pack, the volume of the heating pack is increased significantly with the need for larger amounts of the ferrous material. Presently available designs for heating packs often require a relatively long time to heat up and sometimes produce an undesirable odor.
Several methods of containing a granular chemical composition are presently used for heating packs. Typically, the heating pack container will be a bag-like enclosure having a flap which covers the opening and through which water is added to the granular chemical composition. To suitably contain the granular composition while preventing its spillage, various devices have been utilized, including sealed capsules containing the activating liquid which are punctured for use. In addition, relatively complex funneling apparatus has been used in combination with bags. The sealed capsule type containers generally are not reusable and the complex funnel apparatus results in increased manufacturing costs. Where a simple flap or snapflap design is utilized as the only means for enclosing the chemical composition, the granular material may spill out of the bag. This is particularly so where it is advantageous to shake or agitate the mixture to properly mix the dry chemicals with the liquid.